Fire detector cable



March 21, 1950 G. w. THELIN FIRE DETECTOR CABLE Filed July 20, 1945 1I'll Inventor GeorgeW z-dliwlin WWW W Patented Mar. 21, 1950 UNITEDSTATES PATENT OFFICE rum na'rac'roa can:

Application July 20, 1945, Serial No. .606.172 4 Claims. (Cl. 200-143)This invention relates to the manufacture of electrically conductivefire-detector cables adapted to establish a circuit at any point alongthem where subject to fire and/or undue heating. It aims to provide asimplified and otherwise improved construction for such cables and toimprove the method of manufacture thereof.

In the drawings illustrating by way of example certain embodiments ofthe invention together with means for the manufacture of the articlesconcerned:

Fig. 1 is an enlarged and partly diagrammatic perspective view of ashort length of cable, with the outer conductor broken away in part:

Fig. 2 is a cross-section of the cable of Fig. 1;

Fig. 3 is an elevation of a modified form of the cable; and

Fig. 4 represents schematically one manufacturing method.

In the manufacture of a fire-detector cable as typified in the patent toTurenne 2 ,275,873, dated March 10, 1942, the placing of a multiplicityof separate members of insulating material along a supporting conductorinvolves supply and production problems which it is an object of thepresent invention to eliminate. To that end I provide for the cable aninsulating or conductorspacing means of an endless formation, ofindeterminate length, preferably by the continuous extrusion of asynthetic resinous material.

Accordingly, in the example of Figs. 1 and 2, in which the cable as awhole is indicated generally at i, I have represented at 5 acontinuously extruded length of a plastic or plasticizable substancewhich is non-conductive electrically. is normally flexible at ordinarytemperatures, and is adapted to withstand relatively high temperatures,without undue softening or fusing, that is, subsequent "to extrusion inthe desired form. Otherwise stated, the selected material is thermallystable at least up to the critical temperature of responsive operationfor the cable in the particular circumstances of the intended use.Various suitable materials for the purpose, which, subject to therequirements noted. may be either thermo-plastic or extrudablythermo-setting.

may be selected from the commercially available flexible plasticcompounds.

This elongated plastic strand, body or core element 5 is longitudinal ychanneled externally as generally indicated at 6. Each channel or groove5, as best seen in Fig. 2, has an inner portion 1 providing a continuousseat for a corresponding electric conductor it, a neck or somewhatreduced portion defined by side walls 8, 8, and a laterally open outerportion or mouth 9 at the periphery of the core or carrier 5. In theembodimentof Figs. 1 and 2, the channels 6 are spirally disposed aboutthe core 5, advancing along it in open turns having a substantial leadand relatively flat angle of wind," that is, crossing the core axis atan angle of not more than about 45 at the leading side. The number ofchannels 6, and of conductors It carried in them.

may be varied and the angle of spiralling is in part determined by thenumber of channels and by the relative diameter of the conductors ill.whether one, two or more, three being shown in the illustrated example.With a less numberthe angle of spiral may be increased and the leadreduced. proportionately to reduce the spacing between adjacent pointsof traverse of a channel across any given longitudinal line at theperiphery of the core.

Directly surrounding the plastic core 5 and the laterally open spiralchanneling 6. thereof is a composite flexible electrically conductivetubing l2 comprising an inner layer of a fusible metal or alloy l3 andan outer layer or protective cover of a metal or metallic conductivematerial ll, such as a plating of copper, of relatively high temperatureof fusion as compared with the inner layer. The latter is selected fromthe class of fusible metals and alloys to present the charac teristicfusion point at the critical temperature as appropriate to theparticular use circumstances.

It is noted, particularly with reference to Fig. 2, that the conductorsiii are spaced radially in from the periphery of the core 5,sufficiently for the purposes of electrical insulation, the channelspresenting their laterally open portions or mouths !.adjacent thefusible metal I3. Fusing of the latter at any point along the cable willaccordingly cause the fused metal to enter the adjacent channel orchannels 6 and short circuit the conductor therein across to the tubingi2. As shown, noting particularly Fig. 2, the channel mouths 9 are of awidth to afford ready access for the fused metal to the bare conductorsIt held in the inner seat portions 1 of the channels in distinctlyspaced relation radially inward from the periphery of the non-conductiveflexible synthetic resinous core 5. The normal spacing of the conductorsin from the tubing, the width of the channel mouths 9 and the describedconstruction and arrangement of the core 5 are furthermore such thatbending of the flexible cable as a whole, even upon an arc of smallradius as in installing the cable around a corner, does not causeelectrical contact between a conductor II and the tubing l2.

In Fig. 3 I have shown a further embodiment of the cable of theinvention, wherein the same numerals as in Figs. 1 and 2, with theaddition of a prime mark, indicate corresponding parts. In this instancethe radially open channels or grooves 8' are disposed in generalparallelism to the axis of the plastic core 5', with little or nospiralling. In other respects the construction may be substantially asin Figs. 1 and 2. With the approximately straight channeling of Fig. 3,it is generally desirable to provide a plurality of channels, and thelike number of conductors i0, preferably at least three, in the equallyspaced circumferential arrangement shown, to insure fusion contact atall points along the cable, particularly in horizontal runs thereof.

Manufacture of the cable, of either of the illustrative examples, may inaccordance with the invention be carried out as a single continuousoperation, as schematically represented for instance in Fig. 4. In saidfigure an extruder for the plastic material is indicated at 20. The coreelement 5 issues continuously at the extruding nozzle with the spiral(or straight) channeling 6 simultaneously formed. The extruded core 5 isadvanced continuously past conductor-laying stations, three in theexample shown, at each of which a metal conductor or core in from asupply 22 is laid into a corresponding channel 6. Beyond theconductor-laying stations 22 a strip of the fusible alloy I3 iscontinuously laid along the conductor-carrying core 5, the alloy beingled out from a suitable supply thereof as indicated at 24. l'he workcomprising the alloy strip l3 and the plastic core 5 with the conductorsl0 therein is then passed through a forming die 26 or other meansadapted to fold the alloy strip into tubular form surrounding the core,with the longitudinal side edges of the strip abutted or lapped alongalongitudinal juncture as at Ma. After passing thejorming means 25, thework including the alloy sheathing i3 is advanced in operative relationto a joint-forming or sealing means 30 represented as a heating roll.The latter is maintained at a temperature adequate to soften or partlyfuse the alloy along the Juncture zone [3a adequately to unite theadjoined portions of the alloy into tubing form. In connection with theforming and jointing or sealing steps, or additionally if preferred, thework desirably is somewhat compressed, adequately to bring the channelwalls 8, Fig. 2, into the conductor-retaining but open relationsubstantially as shown. After uniting or sealing the alloy member l3into tubular form a thin plating of copper or other electricalconductive material ll, as previously described, is applied as acovering for the alloy. For this purpose the work is represented in Fig.4 as passing through a plating bath, as at 35. The completed flexiblecable issues continuously from the plating bath, as indicated at theright in Fig. 4, and may be packaged in any convenient manner, as incoils or in cut lengths.

Where the plastic core 5 or 5' is formed or channeled for a plurality ofthe inner conductors such as ll of Fig. 1 and ill of Fig. 3, theindividual conductors preferably are connected in parallel. generally inresistance-balanced relation to the tubular outer conductor and togetherconstituting one side of a detector or signal circuit, as representeddiagrammatically in Fig. 1. There the three conductors it areinterconnected at one or more points along the cable, their common leadbeing connected in a circuit including a suitable source of electricalenergy, an alarm, signal or the like A, and a lead connected to theouter conductive element 13, H of the cable. Similar parallel connectionfor the conductors I. of Fig. 3 and associated alarm circuit will beunderstood. making it unnecessary in Fig. 3 to repeat the circuitdiagram of Fig. 1.

My invention, either as to the articles or the method of making thesame, is not limited to the particular constructions, means or steps asherein shown or described, its scope being pointed out in the followingclaims.

I claim:

1. A flexible fire-detector cable comprising a conductive tubing havingat'least an inner layer of fusible metal, an inner bare metallicconductor, and a nonconducting thermally stable carrier core for suchinner conductor, the core being encompassed by the tubing and composedof an elongated flexible body of resinous material having a laterallyopen channel extending the length of the cable and including an innerconductor-receiving seat, an intermediate conductor-retaining neck and arelatively wide mouth for the inflow of fused metal from the tubing, theinner conductor being positioned in and by the channel seat and neckbelow the core periphery and in spaced relation to the tubing andinstantly accessible via the channel mouth for electrical contact byheatresponsive fused metal from the tubing.

2. A flexible fire-detector cable according to claim 1 comprising aplurality of the channels each having a bare metallic conductor therein.

3. A flexible fire-detector cable according to claim 1 wherein thechannel is disposed spirally along the core.

4. A flexible fire-detector cable according to claim 1 wherein thechannel is substantially parallel to the core axis.

GEORGE WILLARD THELIN.

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS Number Name Date 435.629 Holcombe Sept. 2, 18901,940,917 Okazaki Dec. 26, 1933 2,275,873 Turenne Mar. 10, 1945

